1906.] XERVES OF CHLABIYDOSELACHUS ANGUIXEUS. 979 



was so closely united with the Yagiis that it required very careful 

 dissection for sejDa ration. 



G. The Vagus. 



The Vagus arises by from nine to twelve roots from the hindei- 

 end of the medulla. The laterahs root, which is the most cephalad, 

 is invariably large, the remainder are small. These small roots 

 are not symmetrical in number and arrangement even in the same 

 fish, much less do they agree in difierent fishes. The roots arise 

 at the same level, being arranged in an arc which extends from 

 the side of the medulla to the beginning of the spinal cord. The 

 large lateralis root in one specimen originated 5 mm. in front of 

 the small roots. In another specimen, however, all the roots 

 formed a continuous group. These results both agree with and 

 differ from those of Garman, who states (7. pp. 17 & 18) : " The 

 tenth pair (Yagus) is somewhat asymmetrical, having eight roots 

 on one side and twelve on the other. There are also four pairs 

 of ventral roots near the median line." There were no traces of 

 any median ventral roots uniting with the vagal complex, but 

 there have been so many diflferences in the specimens dissected 

 that too much weight must not be attributed to them. On general 

 grounds, howevei-, it would be indeed interesting to find any median 

 roots going to the Vagus, for although the Vagus is now regarded 

 as a complex of ventral roots, those venti'al roots are regarded as 

 consisting of only visceral sensoiy and motor components. The 

 only nerves which arise in the median position are the third and 

 sixth — that is, two pairs of purely somatic motor nerves. These 

 nerves come from the somatic motor tract, which lies median and 

 ventral. Any other nerves originating in the same region would 

 presumably also be somatic. If Gai"man were right, his specimen 

 suggests the retention of the somatic motor component of the 

 Vagus, whereas, in all cases, so far as is known, the i-emains of that 

 component has passed into the hypoglossal (14. p. 224 seq.). This 

 would indeed be a primitive condition. 



The group of vagal roots passes outwards and somewhat caudad 

 towards the vagal foramen, the separate roots uniting just before 

 they enter the cranial wall. This composite nerve swells into a. 

 large and apparently indivisible ganglion, which lies half in and 

 half outside the cartilaginous wall. Immediately after the union 

 of the vagal roots, two dorsal bi'anches (A and B) are given off". 

 Branch A passes up through the cartilaginous wall and divides 

 therein. The more antei-ior pai-t supplies the neuromasts of the 

 second transverse commissural canal. This is a highly variable 

 nerve, as the neuromasts supplied differed in number from one to 

 five even in the two specimens examined. The other and finer 

 bi-anches of A supply the last inch of the closed canal, i. e. the 

 region between the neuromasts supplied by the Glossopharyngeus 

 and the beginning of the open canal of the trunk. In this region 

 the number of neuromasts supplied vaj-ied from five to eleven. 



